Wireless local area networks (WLAN) for accessing the 3rd Generation Partnership Project (3GPP) evolved packet core (EPC) may be classified into trusted WLAN networks (TWAN) and untrusted WLAN networks. Whether a WLAN network is trusted is determined by an operator. An EPC network is accessed by using a TWAN in multiple modes including a transparent single-connection mode (TSCM). This connection mode is completely based on existing signaling transmission between UE and a WLAN. That is, UE can access a core network EPC by using a WLAN without enhancing any lower-layer signaling for the UE. For the UE, the UE does not sense that the UE accesses a 3GPP core network, and senses only that the UE is connected to a WLAN. This can be implemented without adding any signaling between the UE and the WLAN.
As described above, restricted by the characteristic of the TSCM connection mode, when a packet data network gateway (PGW) in an EPC is overloaded, the PGW sends an overload message to a TWAN, and the TWAN rejects access by UE. In this way, the UE adds, to a blacklist of the UE, a service set identifier (SSID) of the TWAN to which the UE fails to access, and the UE no longer accesses the TWAN. However, the PGW is overloaded, that is, a network status is undesirable only temporarily, and after the network status recovers, the TWAN can still be accessed. That is, the UE wrongly adds, to the blacklist, the SSID of the TWAN to which the UE fails to access because the PGW is overloaded. In addition, because no lower-layer signaling can be enhanced for the UE in the TSCM connection mode, the TWAN cannot notify the UE of a specific access rejection reason.
To avoid this case, in a current 3GPP standard protocol, a TWAN may reselect a PGW for UE to avoid PGW overload, to resolve a blacklist problem caused because access by the UE is rejected without any reason. However, in a process in which a TWAN selects a PGW for UE, a PGW selection mechanism includes a load balancing mechanism. That is, when a PGW is overloaded, another PGW that has a same access point name (APN) is usually also overloaded. Therefore, the current alleviation policy cannot effectively resolve this problem, and in most cases, the UE still adds an SSID of the TWAN to the blacklist.